This section provides background information related to the present disclosure which is not necessarily prior art.
Gas chromatography (GC) is widely used in many industries to separate and identify target analytes, such as volatile organic compounds or semi-volatile organic compounds. GC is particularly useful for analyzing complex samples having multiple target analytes that require individual detection. GC works by observing “peaks” of chemicals passing through a separation column. Thus, a sample having different chemicals or target analytes is introduced via an injector into a packed bed column. Different portions of the sample pass through the column at different rates (due to each chemical's physical and chemical interactions with the material contained in the column). As the target analytes are eluted from (exit) the column, the detector can differentiate the species eluted over time based on the rate at which the analytes pass through the column. Such analytes can be electronically identified and/or quantified during or after the detection.
Micro-gas chromatography is conducted on a miniaturized scale from traditional gas chromatography. One specific type of micro-gas chromatography is comprehensive two-dimensional (2-D) gas chromatography (“GC×GC”). Comprehensive two-dimensional gas chromatography (GC×GC) is well-suited to analysis and separation of complex mixtures of volatile and/or semi-volatile compounds. Generally, GC×GC or comprehensive two-dimensional gas chromatography utilizes two columns of differing selectivities connected in series by a modulator device. In a conventional two-dimensional (2-D) comprehensive gas chromatography (GC) system, the modulator device is placed between the first (1st) and second (2nd) dimensional columns. The modulator device thus sends slices of eluent from the 1st column to the 2nd column, continuously trapping, focus, and re-injecting components eluted from the first column into the second column (as a continuous injector for the second column). The modulator cuts the eluents from the 1st dimension (1D) column periodically (modulation period (PM): about 1-10 seconds) and then re-injects each sliced segment into the 2nd dimension (2D) column sequentially. Consequently, each analyte is subject to two independent separation processes, first by its vapor pressure in the 1D column and then by its polarity in the 2D column. A 2-D chromatogram consisting of the 1D and 2D retention times can be reconstructed by analyzing the eluted peaks detected by a vapor detector installed at the end of the 2D column. Peak capacity is a characteristic of GC systems that describes an overall quantity of peaks that elute—corresponding to the number of discernable chemicals—that can be separated out from a sample by the system. A total peak capacity of GC×GC is nGC×GC=n1×n2, where n1 and n2 are the peak capacity for 1D and 2D separation, respectively. Thus, higher peak capacity is desirable in a GC system.
However, conventional 2-D comprehensive GC suffers from (1) lower peak capacity in the 1st dimension due to the peak broadening during reconstruction caused by sampling; and (2) short 2nd dimensional separation time (and hence lower peak capacity), which is limited by the modulation period (or sampling period). Accordingly, it would be desirable to solve these issues to improve 2-D comprehensive gas chromatography.